This invention relates to environmentally acceptable stabilized vinyl chloride polymer compositions from which arsenic, cadmium, lead, mercury, and thallium are substantially excluded, and to a stabilizer composition for such environmentally acceptable stabilized vinyl chloride polymer compositions to minimize undesirable yellowing and discoloration during the process of fabricating and shaping such compositions into useful articles at elevated temperatures and during the subsequent use of such articles exposed to light.
There is a voluminous literature on the stabilization of vinyl chloride polymers. Patent disclosures of materials stated to be useful in minimizing deterioration of vinyl chloride polymers on heating number well over one thousand. Among the more important heat stabilizers in commercial use are mild alkalis such as sodium carbonate, disodium phosphate, and sodium and potassium salts of partially esterified phosphoric acids; carboxylates and phenolates of zinc, cadmium, and the alkaline earth metals; inorganic and organic lead salts; organotin carboxylates as disclosed by Quattlebaum in U.S. Pat. No. 2,307,157; organotin mercaptides as disclosed by Leistner in U.S. Pat. Nos. 2,641,588 and 2,641,598; various metal-free organic compounds such as the polyols, e.g. mannitol, sorbitol, glycerol, pentaerythritol, organic phosphites, 1,2-epoxides, e.g., soybean oil epoxide, isooctyl epoxy-stearate, and diglycidyl ether of 2,2-bis(p-hydroxyphenyl) propane, and nitrogen compounds, e.g., phenylurea, N,N'-diphenylthiourea, and 2-phenylindole. For detailed discussion of heat stabilizers for vinyl halide resins, reference may be made to the articles, L. I. Nass, in "Encyclopedia of Polymer Science and Technology" (N. Bikales, ed.) Vol. 12, pages 737 to 768 (1970); N. L. Perry "Barium-Cadmium Stabilization of Poly-Vinyl Chloride," Rubber Age 85 449-452 (June, 1959), and by H. Verity-Smith, British Plastics 27 176-179, 213-217, 307-311 (1954); the brochure by the same author The Development of the Organotin Stabilizer (Tin Research Institute, 1959). For a recent summary of the principal types of stabilizers routinely used in vinyl chloride polymers, the disclosure of Kaneko U.S. Pat. No. 4,111,889 of Sept. 5, 1978 can be consulted.
Preponderant in quantity used for many years have been the lead salts, such as tribasic lead sulfate, normal and dibasic lead stearate, dibasic lead phthalate, dibasic leadphosphite, and basic lead carbonates and silicates. Vinyl chloride polymer compositions stabilized with lead compounds are recognized as outstanding in electrical properties and good in color protection during long extended processing at high temperatures, while poor in clarity owing to the insolubility and pigmenting properties of the lead compounds. Next in quantity used have been the organic salt mixtures containing cadmium, as disclosed for example by W. Leistner, in U.S. Pat. No. 2,716,092 of Aug. 23, 1955, G. Mack in U.S. Pat. No. 2,935,491, of May 23, 1960 and J. Scullin in U.S. Pat. No. 3,390,112 of June 25, 1968. Cadmium containing stabilizers have provided excellent heat stability combined with outstanding clarity and resistance to weathering exposure. With the steady increase in usage of vinyl chloride polymer compositions and coincidentally increased concern about the accumulation of toxic materials in the human environment, there has developed a need to replace the lead and cadmium based stabilizers by environmentally more acceptable and no less effective stabilizers. The very favorable properties of the lead and cadmium containing stabilizers, however, have made it difficult to find equivalent replacements. In particular, vinyl chloride polymer compositions stabilized with materials other than lead and cadmium have been subject to objectionable yellowing even where the time to severe heat failure was relatively satisfactory.
J. Darby in U.S. Pat. No. 2,669,548 of Feb. 16, 1954 disclosed halogen-containing resin compositions having improved stability containing a mixture of a zinc salt and a calcium chelate derivative of a 1,3-dicarbonyl compound capable of keto-enol tautomerism. Zinc salts can be zinc salts of organic acids and zinc salts of weak inorganic acids, for example zinc acetate, zinc propionate, zinc octanoate, zinc ricinoleate stearate, and zinc salts of carbonic, silicic, and boric acids. Calcium chelates can be derivatives of betadiketones, betaketoacids, and the esters of betaketoacids, for example the calcium chelates of ethyl acetoacetate, phenyl acetoacetate, acetoacetic acid, acetylacetone, benzoylacetone, and diacetylacetone.
F. Ebel in U.S. Pat. No. 3,001,970 of September 26, 1961 disclosed preventing the discoloration of polymers of vinylidene chloride in light by adding a small amount of a dibenzoylmethane of the general formula: ##STR1## in which R.sub.1 represents hydrogen or a hydroxyl radical, and R.sub.2, R.sub.3 and R.sub.4 represent hydrogen or hydrophobic radicals. Such hydrophobic radicals are for example alkyl, cycloalkyl, aryl, aralkyl and halogen radicals.
British Pat. No. 1,141,971 of May 23, 1967 to W. R. Grace & Co. disclosed zinc complexes of beta-dicarbonyl compounds used as stabilizing additives for chlorine-containing polymers in general, and polyvinyl chloride in particular. The zinc complexes possess the general formula: ##STR2## wherein R and R' are the same or different and are each hydrogen or an alkyl, alkoxy, phenyl or phenoxy group. Preferably when R represents an alkyl or alkoxy group, it contains 1 to 20 carbon atoms.
L. Wiesfeld in U.S. Pat. No. 3,493,536 of Feb. 3, 1970 disclosed that diaroylmethane compounds of the general formula C.sub.6 H.sub.5 CO--CHR--COC.sub.6 H.sub.5 wherein R is hydrogen or a monovalent hydrocarbon radical provide stabilizing action against the sensitizing effect of bismuth or antimony compounds on chlorine-containing materials.
M. Crochemore in U.S. Pat. No. 4,102,839 of July 25, 1978 disclosed the possibility of preventing the thermal breakdown of vinyl chloride polymers by adding 0.1 to 5% by weight of the polymer of one or more carboxylic acid salts of 2-valent metals such as calcium, barium, zinc, lead, or cadmium and 0.05 to 5% by weight of an organic compound having the formula: R.sub.1 --CO--CHR.sub.2 --CO--R.sub.3 in which R.sub.1 and R.sub.3, which can be alike or different, represent linear or branched alkyl or alkenyl groups with up to 30 carbon atoms, arylkyl groups with 7 to 36 carbon atoms, or aryl or cycloaliphatic groups with less than 14 carbon atoms, optionally substituted with halogen atoms, aryl or cycloaliphatic groups, methyl or ethyl groups; aliphatic R.sub.1 and R.sub.3 groups can also be modified by the presence of one or more ##STR3## or taken together represent a 2-valent alkylene group having two to five carbon atoms; also, one of the groups R.sub.1 and R.sub.3 can be a hydrogen atom; R.sub.2 is a hydrogen atom, an alkyl or alkenyl group with up to 30 carbon atoms which can include ##STR4## a group R--CO--R.sub.4 where R.sub.4 is an alkyl group with 1 to 30 carbon atoms or an aryl group when R.sub.1 and R.sub.3 are non-aromatic, or a group having the formula --R.sub.5 --CH(--CO--R.sub.1)--CO--R.sub.3 in which R.sub.5 is an alkylene group with 1 to 6 carbon atoms. The combination of carboxylic acid metal salt and 1,3-dicarbonyl compound is stated to be superior to an equimolar quantity of 1,3-dicarbonyl compound metal chelate.
M. Gay in U.S. Pat. Nos. 4,123,399 and 4,123,400 of Oct. 31, 1978 has disclosed vinyl chloride compositions containing relative to the weight of the polymer from 0.1 to 5% of one of the four pairs of organic salts of the metals Ca-Zn, Ca-Cd, Ba-Zn, or Ba-Cd, the organic salts being salts of saturated or unsaturated, substituted or unsubstituted aliphatic carboxylic acids, or aromatic carboxylic acids, together with 0.05 to 1% by weight of a polyol, and 0.05 to 5 parts of an organic compound having the formula R.sub.1 --CO--CHR.sub.2 --CO--R.sub.3 in which R.sub.1, R.sub.2, and R.sub.3 are defined as by Crochemore, above. Metal organic phosphate ester salts are well known. The range of available products in terms of ratios of esterifying group to phosphate and to metal is indicated, for example, in an article by H. Adler and W. H. Woodstock in "Chemical Industries" for October 1942, pages 516ff. The use of certain salts described by Adler in vinyl chloride polymer compositions is disclosed, for example, by C. E. Huff in U.S. Pat. No. 2,499,503 of Mar. 7, 1950 and by W. H. White in U.S. Pat. No. 2,831,824 of Apr. 22, 1958. W. Leistner in U.S. Pat. No. 2,997,454 of Aug. 22, 1961 disclosed polyvinyl chloride compositions of excellent initial color stabilized with a combination of an organic triphosphite with a heavy metal fatty acid salt to which there is added a phosphorus compound having at least one hydrogen atom of acidic character. The phosphorus acids in Leistner's compositions are defined by the formula ##STR5## In this formula, phosphorus has a valence of three or five, the additional two valences being indicated by dotted line bonds. Typical phosphorus acids coming within this general formula are the following: ##STR6##
In the above formulas R.sub.1 and R.sub.2 represent an organic aliphatic, aromatic or nonaromatic alicyclic hydrocarbon or heterocyclic radical having from one to about thirty carbon atoms. R.sub.1 and R.sub.2 in I, II, III(a) and IV may be the same or different. R. Harrington, Jr. in U.S. Pat. No. 3,274,014 of Sept. 20, 1966 disclosed yarn compositions of synthetic fibers having incorporated a small amount of a metal monoalkyl or monoaryl phosphate, metal dialkyl phosphate, metal alkyl phosphonate, metal alkyl (alkyl phosphonate) or metal dialkyl phosphite are resistant to ultraviolet light. Examples show among others yarns spun from dopes of modified vinylidene chloride-acrylonitrile copolymer containing either zinc (ethyl phosphonate) or zinc bis(ethyl(ethyl phosphonate)).
P. Klemchuk in U.S. Pat. No. 3,219,605 of Nov. 23, 1965 disclosed cadmium, barium, calcium, or zinc salts of monoalkyl phosphites are remarkably effective light stabilizers for polyvinyl chloride compositions, alone or in combination with other light and/or thermal stabilizers. The metal salts are defined by the formula ##STR7## wherein R is an alkyl radical, e.g. alkyl having from 1 to 30 carbon atoms, preferably having from 1 to 12 carbon atoms, and
M is a divalent metal which may be cadmium, barium, calcium or zinc. PA0 "a plastic which has a stiffness or apparent modulus of elasticity greater than 7000 grams per square centimeter (100,000 psi) at 23.degree. C.
Farbwerke Hoechst in French Pat. No. 1,412,321 of Aug. 16, 1965 disclosed the stabilization against light of polyvinyl chloride with 0.1 to 5% by weight of nickel organic phosphites containing only nickel, phosphorus, carbon, hydrogen and oxygen, along with barium-cadmium soaps, organic phosphite, epoxy compounds, and optionally ultraviolet absorbers. T. Kamijo in U.S. Pat. No. 3,312,658 of Apr. 4, 1967 disclosed a stabilizer combination of alkyl-substituted phenolic antioxidant with a synergistic agent which is a nickel salt of a monoester of diester of phosphoric acid, represented by one or both of the formulas: ##STR8## where the R radicals are selected from the group consisting of alkyl, aryl, alkaryl and cycloalkyl radicals.